Because Infrared is a radiant source of heat, it warms the body directly rather than having to warm the air, much like the suns warmth on a cold winters day. There is simply no need for very hot air. Infrared heat stimulates the molecules in our body and increases their vibration causing a natural friction warming effect which penetrates deeply into our tissues spreading the warmth deep in to the body. This process is sometimes called resonant absorption. The result is that a much greater VOLUME of our body is warmed, so our body reacts by working much harder to maintain its optimum temperature through increased sweat production.